Hydraulic fracturing of subterranean formations, also called fracking, is well known. Hydraulic fracturing is a process that uses high pressure fracturing fluid that is pumped into a well to cause the rock formation of the well to separate apart, or fracture, creating pockets within the rock formation. Hydraulic fracturing allows production of oil and gas from areas where other well completion technologies are limited or not possible.
Generally a fracturing fluid is mixed with a proppant and then pumped into a well to create high pressures within the well. After the cracks develop in the rock formations due to the high pressure, the proppant flows into the crack and lodges in place. The proppant stops the crack from closing once the high pressure is released.
The fracturing fluids used in hydraulic fracturing represent varying levels of volatility. Volatility is classified by the vapor pressure and flash point of the fluid. Typically, fluids with a vapor pressure less than 2 pounds per square inch (“psi”) at 100° F. and a flash point greater than 10° F. above ambient temperatures are considered to be non-volatile. Non-volatile fracturing fluids may be open to the environment and therefore may be blended with proppant at a continuous rate through the use of open blenders. Examples of non-volatile fluids include water, low vapor pressure hydrocarbons, and methanol/water mixtures. Volatile fracturing fluids, however, must be processed in an environmentally sealed blender. Environmentally sealed, as used in this context, means that the processing equipment is sufficiently sealed to prevent leakage of gases and particulates from within the processing equipment under normal operating pressures of the equipment.
Until now the only environmentally sealed mixers available were enclosed mixers that only allow for batch processing of fracturing fluid and proppant rather than continuous processing of these materials. Examples of volatile fluids which must be processed in environmentally sealed equipment include liquid carbon dioxide and liquid petroleum gases such as propane or butane.
While non-volatile fracturing fluids are much easier to work with, due to the ability to continuously process the fracturing fluid and proppant in an open blender, a number of additional fluid characteristics must be taken into account which may make the use of volatile fluids more desirable. These characteristics include density, viscosity, vapor pressure, flash point, pH, surface tension, compatibility with formation, reservoir fluid, and cost. FIG. 1 shows relative costs of several common fracturing fluids. FIG. 2 shows relative safety risks of several common fracturing fluids. And FIG. 3 shows relative environment impact risks of several common fracturing fluids.
While the devices heretofore fulfill their respective, particular objectives and requirements, they do not provide an environmentally sealed system for fracturing subterranean formations as such there exists and need for a system for fracturing subterranean formations, which substantially departs from the prior art, and in doing so provides an apparatus primarily developed for the purpose of fracturing subterranean formations in a manner that allows continuous blending and pumping of fracturing fluid and proppant in a manner that is sealed from the environment.